Mrs. Haley, who announced her decision at an early afternoon news conference at the state Capitol in Columbia, said Mr. Scott’s background as a entrepreneur will serve South Carolina well.

“He earned this,” she said.

Mr. Scott, who won a second term to the House last month and will be the only black Republican in the new Congress, was rumored to be Mrs. Haley’s top choice since Mr. DeMint announced earlier this month he will resign from office in January to run the conservative Heritage Foundation.